The present invention relates to the depositing of metal layers or coatings upon the surface of a part or component made of a synthetic or plastic material, and more particularly the invention relates to such a method for depositing metallic layers on fiber re-inforced synthetic material and components made of such a material which are basically hollow but of open construction, possibly having spherically curved surfaces or surface parts, under consideration that the parts are subjected to a material removing treatment as a preparatory step for the depositing or coating process.
Metal foils or sheets are placed upon a carrier body made of a synthetic material, for example, in the art of printed circuit manufacture, using, for example, adhesive bonding to obtain a sufficiently strong connection between support or carrier and the metal foil or sheet. Generally, the support is flat, i.e. planar, and technology for depositing these foils or sheets on such support are adequately developed and do not pose difficulties at the present time. The situation is different, however, when the carrier surface is curved, for example, spherically curved or even of complex curvature such as combined convex and concave surface portions. Here then the depositing of areal metal foil, parts, sheets, or the like, is usually not possible without forming folds or crinkles, assuming, of course, that the curvature is a significant one and is insufficiently approximateable by a straight geometric plane.
Large numbers of parts to be coated or clad, or layered in this fashion, seem to require matching the foil or sheet part to the contour of the surface of the carrier; this in turn, may require shaping the foil or sheet with suitable tools and machines followed by accurate placing and bonding. Basically, this procedure requires tools which are to be matched exactly for that purpose whenever large quantities are involved, these capital layout expenditures may be justified. The situation is different, however, when the number of parts is small. Here then the matching of the contour of the foil or plates to the contour of the carrier or substrate can become very cumbersome and expensive.
Particular difficulties in contour matching of this type will develop when only a portion of the surface of the carrier are to be covered with metal. A simpler approach here is the utilization of electrolytic depositing in order to cover, for example, a part made of non-metal, such as a synthetic part, completely or partially with a metal coating. In the case of fiber re-inforced synthetic wherein the component has, for example, a curved surface portions, the depositing of a metal coating by means of electrolytic technique requires initially to render the surface of the synthetic part electrically conductive so as to be able at all to obtain electrolytic deposition of metal thereupon.
Certain materials having supporting functions generally, such as load bearing structure parts in aircraft, airborne vehicles, and analogous crafts, require, of course, a dimensioning that is dictated primarily by the expected load. Such part has to take up, while, on the other hand, low weight is a highly desirable feature in the aerospace industry. With this as background one has to consider the possibility that some of these parts have curved surfaces spherical or complex ones, at least in parts, and one may invision a structural material being comprised of fiber reinforced epoxy resin. Such a part, for example, may require to be coated in parts with metal to function as a transmission or receiving antenna. Here then specific problems arise concerning adequate adhesiveness of the coating, owing to the formation of a skin made of a separating material and which remains depositing on the surface of a part after it has been manufactured; the manufacture process of fiber re-inforced synthetic parts often requires such separation. The separating material, on the other hand, will prevent adequate adhesion of the subsequently deposited metallic coating, and surprisingly the usual cleansing methods are insufficient to really completely remove such separating material.
Generally speaking, particular methods are used for mechanically and/or chemically surface treat a part in order to prepare it for coating. What is involved here is actually the removal of a thin surface layer for cleaning purposes. Here then the danger exists, irrespective of the effectiveness of this cleaning, that the surface as such is being damaged in the cleaning process. This is particularly the case when the surface is primarily formed of a synthetic material. But also re-inforcing fibers which are close to the surface may be cut or otherwise damaged. Such a damage, even though seemingly minimal, may, in fact, interfere with the strength requirements. This is a particularly important feature if the part is expected to take up significant load and when weight constraints preclude excess dimensions. The problem actually is compounded if a partial coating is required only so that only parts of the surface of the component is so treated and, therefore, subjected to strength interfering damage, etch-treating surface portions which will not be covered by a coating subsequently is undesirable for a variety of reasons. In order to avoid the cleaning of surface parts which are not to be coated, these are covered by ribbons or the like prior to etch cleaning, in order to avoid exposure to the cleaning agent. These partial surface coverings, however, again are difficult to accomplish for reasons of the curvature. Access to the interior of the parts may be difficult or even impossible.